The present invention relates to tubing for use in a motor vehicle. More particularly, the present invention relates to a multi-layer tube which can be employed for transporting hydrocarbon fluids. For example, the multi-layer tube may be used as a fuel line and/or vapor recovery line of a motor vehicle.
Single layer fuel lines and vapor return lines of synthetic materials such as polyamides have been proposed and employed in the past. Fuel lines employing such materials generally have lengths of at least several meters. It is important that the line, once installed, not materially change during the length of operation, either by shrinkage or elongation or as a result of the stresses to which the line may be subject during use.
It is also becoming increasingly important that the lines employed be essentially impervious to hydrocarbon emissions due to permeation through the tubing. It is anticipated that future Federal and state regulations will fix the limit for permissible hydrocarbon emissions due to permeation through such lines. It is also imperative that the fuel line employed be impervious to interaction with corrosive materials present in the fuel such as oxidative agents and surfactants, as well as additives such as ethanol and methanol.
Various types of tubing have been proposed to address these concerns. In general, the most successful of these have been co-extruded multi-layer tubing which employ a relatively thick outer layer composed of a material resistant to the exterior environment. The innermost layer is thinner and is composed of a material which is chosen for its ability to block diffusion of materials, such as aliphatic hydrocarbons, alcohols and other materials present in fuel blends, to the outer layer. The materials of choice for the inner layer are polyamides such as Nylon 6, Nylon 6.6, Nylon 11 and Nylon 12.
Alcohol and aromatics in the fluid conveyed through the tube diffuse at different rates through the tubing wall from the aliphatic components. The resulting change in the composition of the liquid in the tubing can change the solubility thresholds of the material so as, for example, to be able to crystalize monomers and oligomers of materials, such as Nylon 11 and Nylon 12, into the liquid. The presence of copper ions, which can be picked up from the fuel pump, accelerates this crystallization. The crystallized precipitate can block filters and fuel injectors and collect to limit travel of the fuel-pump, as well as build up on critical control surfaces of the fuel pump.
Heretofore it has been extremely difficult to obtain satisfactory lamination characteristics between polymer layers comprising an inner tubing substrate and an outer jacket layer Such lamination or bonding may be quite important to prevent slipping of an outer jacket layer with respect to an inner layer during assembly of connectors or the like to the inner tubing substrate. In the industry, fuel and/or vapor line barbed connectors are inserted firmly into the interior opening of the inner tubing substrate. However, if the connector is not inserted properly, it may during insertion abut the radial thickness of the inner tubing substrate. On occasion, it has been found in such circumstances that the inner tubing substrate may slip back within the outer jacket, unbeknownst to the assembly worker. As such, the overhang of the outer jacket past the terminated end of the inner tubing substrate may mask or hide an incorrect and/or incomplete assembly of the connector into the end of the inner tubing substrate. As can readily be appreciated, such an incorrect assembly of the connector to a fuel and/or vapor line may result in undesirable leakage of fuel and/or vapors.
In order to correct this potential problem, attempts have been made to glue and/or adhere an outer jacket to an inner tubing substrate. However, during the crosshead extrusion of a polymeric outer jacket onto an inner tubing substrate, the temperature may reach about 350.degree. F. or higher. At this temperature, conventional glues, adhesives and the like burn off, flash off and/or otherwise decompose undesirably. In addition to failing to provide suitable bonding between an outer jacket and an inner tubing substrate, the use of conventional glues, adhesives and the like may adversely affect the inner tubing substrate and/or the equipment used during the process.
Thus, it is an object of the present invention to provide tubing which could advantageously be employed in motor vehicles, wherein the tubing is composed of at least an inner tubing substrate layer and an outer jacket layer, wherein the two layers are sufficiently bonded to advantageously substantially prevent slipping therebetween. It is a further object of the present invention to provide an extrudable adhesive between the two layers, which adhesive advantageously becomes tacky during crosshead extrusion of the jacket layer thereover without running off, burning or flashing off. It is yet another object of the present invention to provide tubing which would be durable and prevent or reduce permeation of organic materials therethrough. It is a further object of the present invention to provide tubing which would be essentially nonreactive with components of the liquid being conveyed therein. Still further, it is an object of the present invention to provide tubing which would advantageously be capable of preventing the buildup of electrostatic charge therein and/or would be capable of safely dissipating any electrostatic charge induced therein.